Variable frequency oscillator



Feb. 11, 1947. A. L. 6. DE BEY 2,415,457

VARIABLE FREQUEQCY OSCILLATOR Filed Jan. 5, 1943 Paiented Feb. 11, 1947 VARIABLE FREQUENCY OSCILLATOR Albert L. G. 'de Bey, Aberdeen, Md, assignor to Purdue Research Foundation, West Lafayette, Ind, a corporation of Indiana Application January 5, 1943, Serial No. 471,315

Claims. 1

This invention is directed to electronic apparatus and particularly to electron tube oscillators.

In its preferred form, the invention consists of the use of a plurality of thermionic tubes connected in an electrical network so as to generate any desired frequency within reasonabl limits, depending upon a change of the value of one of resistance or capacity elements.

Essentially, the complete network herein to be isclosed comprises an oscillator wherein various couplings are provided from circuits which include only resistance and capacity elements whereby extremely stable operation is obtained and the desired phase shifts are readily accomplished.

In its preferred form, the invention is particularly adaptable to use in connection with the generation of frequencies within predetermined limiting values where the generated frequencies may be transmitted to remote apparatus for the purpose of controlling it.

One such use of such remote control is provided in the generation of signal energy of frequencies varying between two predetermined limiting values, and which may be transmitted then to control, in an appropriat manner, such remote apparatus so as to make the apparatus function in accordanc with some pre-established operation at a control point which serves to produce the desired frequency.

Essentially, the arrangement herein to be described is one wherein different frequencies are adapted to be generated under the control of a controlling instrumentality which represents the control element of an airplane, so that by varying the control element within predescribed limits, corresponding to those limits which would be used for changing the position of the plane from a maximum climb position to a maximum dive posi tion, or from a maximum turning in one direction to turning in the other direction, the oscillator frequency may be caused to change between the desired limits. Energy of the generated frequency, which will then be proportional to the change in position of the controlling instrumentality, may be radiated to an airplane, for instance, so that when received in suitable discriminator networks, the elevators or the rudder, or ailerons of the remotely controlled plane may be varied in order that the plane may be guided in its flight path solely under the influence of the signals received from the ground or controlling station.

In a companion application, Serial No. 369,216, filed December 9, 1940, a system was proposed whereby the flight path of an airplane might be controlled from a ground station when trans- Ifl mitted frequencies, varying between predescribed limiting values, were generated and transmitted to the plane, so that the plane elevation or turning might be suitably controlled.

The present invention is directed primarily to the oscillation generator whereby the desired control frequencies are established and generated.-

In the preferred form of arrangement, there is provided at the control station, a suitable control stick which will correspond to the control stick normally to be handled by the pilot of the aircraft and, according to the forward or backward position of the control stick, varying frequencies are generated for controlling the planes flight in a vertical path, for instance, and, in accordance with the motion of the control stick to the right or to the left, other frequencies, varying between predescribed limits, are produced and transmitted to control the planes position in the horizontal path, for example, its turning as contrasted to its climb or dive, and the plane then may be guided from the control station to desired locations completely from a remote source.

Accordingly, it becomes an object of this invention to provide a control oscillator for generating the controlling frequencies, which oscillator shall be extremely stable in character so that the controlled instrumentality shall likewise retain normal position with great stability.

Other objectsof the invention are those of providing an oscillator in which the controlled frequencies may readily be adjusted within reasonable limits merely by the variation of one of a resistance and a capacity element,

A further object of the invention is that of developing an oscillator which will operate over the range of audible and super-audible frequencies with the frequency capable of being controllably continuously varied over the desired range.

A still further object of the invention is that of providing an oscillator whose output energy shall be substantially pure sine wave so as to prevent the development of harmonics which would interfere with adjacentcontrol channels.

Still other objects of the invention are those of providing an oscillator highly efficient in its use, and an oscillator which is substantially free from drift, even during the warm up period and under conditions of variations in the supplied energy, and which, at the same time, shall have a substantially constant output or amplitude over its operating range.

Other objects and advantages will become apparent from a reading of the following specifica- 3 tion and claims, taken in connection with the accompanying drawing, wherein:

Fig. 1 shows schematically one suitable form of circuit; and

Fig. 2 is a diagram to illustrate rather generally the principles of operation.

Referring now to the drawing, the oscillator, in its simplest form, comprises a plurality of thermionic tubes H, I2, l3 and M having included therein cathode elements l5, i6, 11 and N3, of which the cathode elements of the first two tubes II and i2 are preferably connected together by way of the conductors l9 and-20, and thence connected to ground 2| througinaresistance 22. Similarly, the cathodes l1 and I8-.of the tubes l3 and I4 are connected together through the conductors 2i and28, and'likewi'se connect to ground 2| through a cathode .bias resistor 29.

It willhereinafter be shown how the oscillations in the described circuit are developed, but, for the moment, it may be assumed that the arrangement to be described is so constituted that the cathode resistor 29 may serve as the leadresistor for the output circuit, so that the output energy from the complete combination may be derived at terminals 313 and'3i, of which the terminal 30 connects to the cathodes l7 and i8 and the upper end of the resistor 29 by way of a conductor '32, and the opposite terminal 3| connects to ground at 2!. 'In this way, the outputenergy is derived from the coupling across the cathode resistor .29. 7

Each of the tubes H through 14 inclusive also includes a control electrode 4i 41,42 and43, of which the control electrodes ll and G3 are preferably connected to ground "2i by way of conductors '44 .and 45. The anode or plate elements 50, 51,152 and 53 of the tubes H through l4 inclusive are supplied'with energy from a source of voltage, not shown, which is connected at the terminal point '55 and supplied to the various tube anodes orplates through the resistors 55, '1, 58 and 59. Inthe instance shown, the resistors 51 and 59 are usually slightly more than twice as large as the resistors .56 and 58 in order that a'higher voltage may be developed across the output resistor 29.

'The foregoing, however, represents only one possible working condition, and, accordingly, it

shouldi be understood that the finally chosen constants.- or parameters in any particular circuit are determined by the adjustment necessary to cause the a. 0. plate voltages, as measured from the anodes 50 andfil, or52 and 53, to ground 2!, to be substantially alike. Because of the phase inverter operation of the pair of tubes, the excitation or the driving voltage to the grid of the tube 12, for instance, is not the same as that of the tube H, and generally, it is desirable toincrease the plate load resistances of the tubes 12 and M in order to bring their output up to that of the tubes H and I3. The adjustment, under some circumstances, is rather critical for optimum operation of the phase shifting circuits, but, as far as the output circuit or circuits comprising the resistors 29 and/or 22 are concerned, this adjustment does not appreciably aiiect the output voltage.

,Also connected between the plate elements 50 and 5| :of the tubes H and i2 is a'circuit comprising resistance and capacity elements, which includes, for instance, in sequence between the plateoranodeiiland the plate 'or anode 5!, the combination of a capacity Bil, a plurality of reth n? 4 sistors 62, 64, 66 and 68 with a condenser 10 making connection to the anode or plate 5i.

The outer terminals of the condensers iii) and I9 remote from the resistances 52 and 68 respectively connect also to the end of the resistors 56 and 51 which supply the plate or anode voltage to the. tubes H and 12.

A connection to ground 21 is provided intermediate the resistors 64 and it so as to provide a balancing of the network.

Intermediate the resistors 62 and 64 a connection is made to a condenser '12 which is connected in series with a fixed resistor 14 and a variable resistor .01 potentiometer T6, the op- "sposite ;terminal of which is connected intermediate the resistors 66 and 68, and at a junction point "Blintermediate the condenser 12 and the resistor Hi a connection is made by way of the conductor 83 to the control electrode 42 of the tube l3 to feed the energy from the output of the combination of the tubes II and [2 into the tube l3.

In a manner similar to that explained in connection with the tubes H and I2, a suitable network, comprising capacity and resistance elements, is connected between the plates or anodes 52 and 53 of the tubes 13 and 4 with a connection being from the anode or plate'52 through a condenser 'Bl, aplurality of resistors 63, -65, El and B9, and thence to a condenser ll which connects in turn'to the plate or anode 53 of the tube l4.

As was explained in connection with the tube combination H and :2, the junction of the resistors 65 and 61 is connected to ground at 2| and likewise a condenser 13 has one terminal connected to the junction-of the resistors 63 and 65 with its other terminal connected to the series combination consisting of the fixed reistor 15 and the variable resistor or potentiometer 11 which connects to the junction of the resistors 61 and 69 in a manner similar to the connection of the resistor or "potentiometer "16 to the vjunction of the resistors 66 and 68.

"The conductor a l connects intermediate the capacity 13 and the resistor l5 to provide a feedback of the energy appearing at the connection point to the control electrode 40 of the tube l I.

Thecondensers BI and H, like the condensers 60 and '10, connect at one terminal also to the resistors 58 and 59 which supply the positive potential for the anodes or plates 52 and 53 of the tubes [.3 and I4.

In order that the frequency of oscillations developed'in the system maybe varied, the'unicontrol, conventionally represented atilll, is'provided to vary simultaneously the resistance values of the potentiometers 16 and'fl, and such variation is assumed to be the variation due to one motion, for instance, the backward and forward motion by the control element, so that it, iorfiinstance, might control the elevator channel or, where desired, the variance of the potentlometers 75 and H may-be providedby the lateral motion .by the control element to cause the rudder .channel frequency to be changed to vary the horizontal position.

In the Way in which the arrangement has been shown, no provision is made for indicating the power supply, but such a supply unit is generally included and connected to the terminal 55. In this connection, the stability ofthe oscillators II through I4 inclusive is usually. extremely ood, so thatcaccurate regulation .of .thepower supply is not generally required.

- The output energy, as derived at the terminals 30 and 3 l,is preferably fed to a suitable amplifier stage which is then preferably transformer-coupled to a low impedance line, and where desired, a suitable Vacuum tube voltmeter may be connected across the transformer secondary output to measure the output of the oscillator energy to serve as a modulation indicator.

The tubes ll, I2, l3 and I4, herein illustrated for the purpose of a schematic showing, are indicated as separate tubes, although it is to be understood that the tubes II and 12 may, where desired, be incorporated within a single envelope and the tubes l3 and 14, for instance, also be incorporated in a single envelope, such being, for example purposes only, the general type of tubes known in the art as the 6F8-G.

In considering the above described apparatus, reference might be made, for instance, to the so-called resistance-capacitance phase shifting networks for a further understanding of the principles of operation. In resistance-capacitance phase shift circuits it is known that the necessary 180 phase shift for the feedback to the grid or control electrode of a tube to cause it to oscillate can be obtained. Furthermore, as long as the feedback is suiiicient, any change in the value of either the resistances or the capacitances of the phase shift circuit will cause the frequency to change until the phase shift is again 180. Thus, it becomes apparent that frequency can be made a function of either or both the value of the resistance or the capacitance, and that the frequency may be varied byvarying one or both of these elements.

Under normal circumstances, .a single condenser and resistance in series does not provide quite a 90 phase shift, and therefore, to obtain the necessary phase shift, usually three capacityresistance circuits are required. However, by taking recourse to an arrangement wherein ene y is supplied, for instance, to the secondary winding of a transformer, one of whose outer terminals connects to a condenser and the other of whose outer terminals connects to a resistance, with the resistance and condenser connected together so as to form a series network and with the output terminals taken from the midpoint of the transformer secondary and the junction of the condenser and the resistance, practically the desired 180 phase shift can be obtained. If either the value of the capacity or the resistance becomes very large, the output voltage at the terminals above described approaches that voltagebetween the center tap of the transformer secondary and the outer terminal which connects to the condenser, while, if both the capacitance and the resistance become very small, the output voltage at the output.terminals above described approaches that existing between the center tap of the transformer secondary and the outer terminal which connects to the resistance, and is 180 out of phase with the first described Voltage. With the present arrangement, as particularly shown by Fig. 1, the general principles above set forth have been relied upon to some extent. In this connection, the condensers 60 and 10 on the one hand, and BI and H on the other hand have been made large compared to the condensers l2 and 13 respectively, so that the condensers 60 and 10, as well as BI and H, first named, have the effect in the system of blocking the direct current plate voltage from the grid or control electrode circuit of the next stage of the system. Q'Theiresistors, designated in Fig. lgenerally as '6 62, 64, 68 and 68, and then also as 63, 65, B! and 69, serve generally to provide a grid return to ground and to act somewhat in the nature of a potentiometer to reduce the driving voltage to the next stage, it being noted that distortion is apt to be caused if the tubes are over-driven.

Referring now more particularly to the diagram of Fig 2, which is merely one of several possible'illustrative explanatory diagrams, it may be assumed that the voltage represented as the vector oe4o, which occurs at some arbitrary frequency ,f, is applied to the control electrode or grid 40 of the tube l I. This obviously would provide a plate or output voltage at the plate or anode 50 of the tube II which might be represented as the voltage designated by the vector By reason of the connection of the grid or control electrode 4| of the tube l2 to ground at 2|, and by the connection of the cathode Hi to ground through the cathode resistor 22, it will be understood that when voltages of the above named orders are applied to the tube 1!, the effect will be substantially as if there were a voltage applied to the grid or control electrode 4| of the tube l2, and this voltage may be represented as the voltage shown by the vector oe41, as in Fig. 2. The resulting output voltage from the tube 12 would be 180 out of phase with the control voltage and then might be represented by the vector 0e51 which would be the voltage appearing at the anode or plate 5| of the tube l2 for the assumed input.

As was above indicated and pointed out in connection with the explanation of the theoretical circuit comprising the transformer secondary whose end terminals connected with a series network including the capacity and resistance element, if a capacitance l2 and a resistance represented by the fixed resistor 14 and the potentiometer I6 is connected between the plate or anode electrode 50 of the tube l I and the plate or anode 5| of the tube l2, it will be appreciated that for some particular value of resistance and capacity, the resistance drop, designated as IBM-76 will be equal to the reactance drop 1X72- at the frequency f, hereinabove assumed. Accordingly, the voltage which is applied to the grid or control electrode 42 of the tube l3 by reason of its connection through the conductor 83 to the junction point of the condenser 12 and the resistor 14, will lead the voltage applied to the grid or control electrode 40 of the tube 1 i by as represented by the vector and voltage o-e4z in Fig. 2.

Similar to the description above set forth, the voltage appearing at the plate or anode 52 of the tube l3 may be represented by the vector o-e52 in Fig. 2, and the phase inverter tube It will then operate as though it had a voltage, represented by the vector oe43, applied to its grid or control electrode 4! following the analysis hereinabove explained with regard to the tube I2.

Likewise, the voltage appearing at the plate or anode 53 of the tube it may be represented then by the Vector 0e53.

If, now, it be assumed that a capacitance I3 and-resistance elements 15 and TI connect between the plates or anodes 52 of the tube l3, and 53 of the tube M, andthat these elements are so chosen that the conditions set forth are maintained, namely, that IR'15-77 is equal to 1X13, it will be apparent that the voltage which is fed back by way of conductor 84 to the grid or control electrode 40 of the tube II will be in phase 7 with the originally assumed voltage, represent ed by the vector (were, and may be substituted for it. Sincethis voltage is out of phase with the plate voltage, re resented by the vector oeo, it is a parent the [system will oscillate. The dotted lines on Fig. 2 have appropriate legend-s applied to show the different voltage drops taking lace, as, hereinaboye explained. a

From what has been above pointed out, it will be noted that under conditions where the ratio of IBM-76 to IR75-77 equals the ratio of 1X72 to 1X73, and where IBM-'16 equals 1X12, and similarly IRcs-"n equals IXvs, the oscillator disclosed by Fig. 1 will produce two-phase push-pull voltages by connecting between the plates or anodes 50-51 and 52'53, or tour-phase single ended, by connecting from each of the above plates or anodes to ground. I 1

In connection with the ty e or circuit hereinabove explained, it might be pointed out that oscillations at any frequency for which the total phase shift in the two circuits is 180 may be sustained, regardless of whether the phase shift is equal in the two circuits. Furthermore, in connection with the development of sinusoidal wave form, it is desirable that the feedback be adjusted to a value approaching the minimum that will sustain continutuis oscillation, with the circuit of Fig. 1. By adjustment and variance of the ratio of the voltage dividers formed by the resistors 62-45% and "66-'88, for instance, the feedback may be varied and adjusted to an desired value. The resistors s2, 64 and 66, 68, for instance, form a voltage divider circuit from plates 50, ii of tubes H and 12 to ground. The arrangement is similar for tubes l3 and 4. The adjustment and variance of the ganged and unicontrolled potentiometers l6 and i1 control the frequency at which the oscillator "will sustain oscillations and the frequency may be varied, since these elements form a part of the phase shift circuits.

The fixed resistors, represented at 14 and 15, are particularly useful in this connection as providing a series in resistance with the potentiometer and, as shown, it is clear that the possibility of removing all of the resistance in the circuit at the time when the value of the resistance in the potentiometers l6 and T"! is reduced to a minimum, which would tend to introduce a comparatively large capacity to ground, is avoided. The introduction of such a capacity effect would, in turn, cause the output voltage to vary greatly with small changes in the resistance and capacity and thus make the system unstable.

Generally speaking, tubes with low plate re- Sistance are best suited for use in connection with the oscillator hereinabove explained because such tubes perrnit obtaining the required gain for oscillation with low values of load resistance, with the result that the shunting effect of the phase shift network does not cause any appreciable change in the effective load on the tubes. In this way, the gain is stabilized and substantially constant output voltages are derived across the output resistor 29 and caused to appear at the output terminals 3tand 3i. In order to obtain a higher voltage output across the resistor 2d, it is preferable to have the resistance values 5? and 59 somewhat in excess of those of resistors 56 and 58, as hereinabove pointed out.

In connection with the illustration of Fig. 1-, it is important to note that inductance elements may be substituted for capacity elements in the phase shifting networks of the circuits. For instance, the capacitors Hand. 13 might be replaced by inductors, in which event it will be apparent that the efiects may be obtained by either series inductance and resistance or series capacitance and resistance. Interchangin'g the order of the capacitance and resistance elements to become, for instance, resistance and capaci tance, or resistance and inductance, as the case may be, has the effect of shifting the phase "of the output voltage by 180, and this may readily be done where desired, providing the change is made in the output circuit of each pair of tubes in like manner.

It should be noted further in connection with the circuit herein described, that it is capable of generating multi-phase voltages by connecting an output circuit, such as that shown at .30 and 3| for instance, also across the cathode re= sister 22 of the tubes l l and I2, which would produce an output voltage which is out of phase by with regard to that output voltage which appears across the resistor 29, so that a twophase oscillator may be developed. If it is desired to use three pairs of tubes and three phase shifting networks in the system, for instance, a three-phase oscillator may be produced with a. phase shift of 60 between each of the voltages. It, of course, must be borne in mind that it is desirable to adjust the phase shifting networks very carefully and closely in order to make the voltages the exact phase dili'erence that is desired.

While the invention hereinabove explained has been shown in one of its preferred forms, it is, of course, apparent that various modifications may be made, provided such modifications fall fairly and clearly within the spirit and scope of what is hereinafter set forth and claimed.

Having described my invention, what I claim as new and desire to have protected by Letters Patent is:

1'. A closed electrical network comprising a plurality of pairs of thermionic tube elements each including an input and an output circuit, a phase shifting electrical circuit including series con-- nected reactance and resistance elements connected in parallel with the output circuits of each pair of thermionic tube elements, means for supplying energizing potentials to one tube ele ment of each pair in accordance with the voltage appearing at the junction of each series reactance and resistance element, and means to supply the other tube element of each pair withcontrol en'- ergy from the controlled tube of each pair,

2. An oscillation generator comprising a plurality of pairs of thermionic tube elements each having input and output circuits, a plurality of electrical networks each including series connect ed reactanc'e and resistance elements connected in the output circuits of each pair of thermionic tube elements, means for supplying energizing potentials to one tube element of each pair in accordance with the voltage appearing at the junction of each seriesreactance and resistance element, means to supply the other tube element of each pair with control energy from the com plurality of pairs of thermionic tube elements each including an input and an output circuit, a

phase shifting electrical circuit including series connected capacity and resistance elements connected in parallel with the output circuits of each pair of thermionic tube elements, means for supplying energizing potentials to one tube element of each pair in accordance with the voltage appearing at the junction of each series capacity and resistance element, and means to supply the other tube element of each pair with control energy from the controlled tube of each pair.

4. An oscillation generator comprising a plurality of pairs of thermionic tube elements each having input and output circuits, a plurality of electrical networks each including series connected capacity and resistance elements connected in the output circuits of each pair of thermionic tube elements, means for supplying energizing potentials to one tube element of each pair in accordance with the voltage appearing at the junction of each series capacity and resistance element, means to supply the other tube element of each pair with control energy from the controlled tube of each pair so that the said tubes last named-are each energized in an out-of-phase manner relative to the controlled tubes, whereby the tubes form a closed network and regeneration takes place, and a load circuit to derive output energy from said circuit.

' 5. An electrical oscillator comprising a plurality of pairs of thermionic tubes each having an input and an output circuit, means for energizing the second tube of each pair under the control of the first tube of each pair so that the energy output i out-of-phase with the output of the first tube of each pair, a phase shifting network comprising series resistance and reactance elements connected between the output circuits of each of the pairs of tubes, an electrical connection to the junction of the series reactance and resistance elements for supplying energizing potentials to the first tube of each pair which are out-of-phase by a predetermined amount with the preceding tube, and means to vary one of said reactance and resistance elements of each phase shifting network to vary the natural oscillation frequency generated.

6. An electrical oscillator comprising a plurality of pairs of thermionic tubes each having an input and an output circuit, means for energizing one tube of each pair under the direct control of the other tube of each pair so that the energy output is out-of-phase with the output of the first named tube, a phase shifting network comprising series reactance and resistance elements connected between the output circuits of each of the pairs of tubes, a direct connection between the junction of the series connected reactance and resistance elements and the uncontrolled tube of the pair whereby oscillations are generated, means to vary one of said resistance and reactance elements of each phase shifting network to vary the natural oscillation frequency generated, and a load circuit to derive output energy from said oscillator.

'7. An electrical oscillator comprising a plurality of pairs of thermionic tubes each having an input and an output circuit, means for energizing .the second tube of each pair under the control of the first tube of each pair so that the energy output is out-of-phase with the output of" the first'tube of each pair, a phase shifting network comprising series resistance and capacity elements connected between the output circuits of each of the pairs of tubes, an electrical connection to the junction of the series capacity and resistance elements for supplying energizing potentials to the first tube.

- work to the input circuit of a tube of a different pair to control thereby the output energy from of each pair which are out-of-phase by a predetermined amount with the preceding tube, and means to vary one of said capacity and resistance elements of each phase shifting network to vary the natural oscillation frequency generated.

8. An electrical oscillator comprising a plurality of pairs of thermionic tubes each having an input and an output circuit, means for energizing one tube of each pair under the direct control of the other tube of each pair so that the energy output is out-of-phase with the output of the first namedv tube, a phase shifting network comprising series resistance and capacity elements connected between the output circuits of each of the pairs of tubes, a direct connection between the junction of the series connected capacity and'resistance. elements and the uncontrolled tube of the pair whereby oscillations are generated, means to vary one of said resistance and capacity elements of each phase shifting network to vary the natural oscillation frequency generated, and a load circuit to derive output energy from said oscillator.

9. An electrical network comprising aplurality of thermionic tube elements, each of said tubes.

having an input and an output circuit, an electrical control circuit including series connected capacity and resistance elements connected in the output circuits of predetermined pairs of said thermionic tube elements, means for supplying energizing potentials developed in accordance with the voltage appearing at the 'junction of each series .capacity and resistance element of each series network to theinput circuit of a tube of a different pair to control thereby the output energy therefrom, means to supply theother tube element of each pair with control energy from the controlled tube of each pair, whereby the plu-. rality of tubes is connected tov form a closed network and regeneration takes place to produce oscillations, and a load circuit to derive output energy from said circuit.

10. The system and network claimed in claim 9 comprising, in addition, means to vary simultaneously the resistance element of each network to alter the natural oscillation frequency of the network.

11-. An electrical network comprising a plurality of thermionic tube elements each having an input and an output circuit, an electrical control circuit including series connected reactance and resistance elements connected in the output circuits of the predetermined pairs of thermionic tube elements, means for supplying energizingpotentials developed in accordance with the-voltage appearing at the junction of each series reactance and resistance element of eachseries netthe said energized pair, mean-s to supply the othertube element of each pair with control energy of the controlled tube of each pair so that the plurality of tubes is connected to form a closed network and regeneration takes place to produce oscillations, means to vary simultaneously. one ofthe resistance and reactance elements of, each series network to alter-thereby the natural oscillation frequency of the network, and means congnected to predetermined pairs of said tubesto derive output Voltages of predetermined phase relationship with *respect to the voltages of other tubes.

12. An oscillator comprising two pairs of thermionic tubes each having an input circuit and an output circuit, means for energizing the input circuit of one tube of each pair under the 11 control of the energy flow in the. other tube of each pair so that the energy output of the said tubes is out-of-phase, a phase Shifting network,

comprising series resistance and capacity ele ments connected between the output circuits of thetubes of each of the said pairs, an electrical connection to the junction of. the series capacity and resistance elements of the phase shifting network for supplying energizing potentials to the tube of the other pair of tubes which is free from direct. control by the other tube of the pair to apply an energizing voltage which is out-ofphase relative to the similar tube of the other pair, whereby a closed network results and elec trical oscillations are generated, and means to vary the resistance elements of each phase shifting network to vary the natural oscillation frequency generated.

13. An oscillator comprising two pairs of thermionic tubes each having an input circuit and an output circuit, means for energizing the input circuit of one tube of each pair under the control of the energy flow in the other tube of each pair so that the energy output. of the said tubes is out-of-phase, a phase shifting network comprising series resistance and capacity elements connected between the output circuits of the tubes of each of the said pairs, an electrical connection to the junction of the series capacity and resistance elements of the phase shifting network for supplying energizing potentials to the tube of the other pair of tubes which is free from direct control by the other tube of the pair to apply an energizing voltage which is out-ofphase relative to the similar tube of the other pair, whereby a closed network results. and electrical oscillations are generated, andmeans to vary simultaneously the resistance elements of each phase shifting network to vary the natural oscillation frequency generated.

14. A thermionic oscillation generator comprising thermionic means having iour independent electron paths each including at least an anode, a cathode and a control electrode, an electrical connection between the cathode elements of the first and second of said electron paths and the cathode elements of the third and fourth of said electron paths, means to bias said cathodes relative to a point of predetermined potential, means for supply operating voltages to the anode elements included within each electron path, a connection between each anode element and the said point of predetermined potential comprising series connected capacity and resistance elements, a phase shifting network comprising an electrical network including series connected capacity and resistance elements connected between a predetermined point on the resistor element which is connected between the anode of the first electron path and said point of predetermined potential and a predetermined point on the resistor connected between the anode of the second electron path and said point of predetermined potential and a second phase shifting network also including series connected capacity and resistance elements connected be tween similar points on the said resistance elements which are connected between the anodes and the point of predetermined potential of the third and fourth electron paths, a connection from. the junction point of the capacity and re.-. sistance elements of each of. said electrical networks. to the control electrode. included within one electron path of each of the pairs, a connection between the. control electrode of the uncontrolled electron path to the point of predetermined potential, and means for simultaneously varying the value of one of said resistance. and capacity means of said series phase shifting networks to. alter thereby the oscillation frequency developed.

15. A thermionic oscillation generator comprising, thermionic means having four independent electron paths. each including at least an anode, a cathode and a control electrode, an electrical connection between the cathode elements oi the first and second of said electron paths and the cathode elements of the third and fourth of said electron paths, means to biassaid cathodes relative to a point of predetermined potential, means for supplying operating voltages to the anode elements included within each electron path, a connection between each anode element and the said point of predetermined po-- tential comprising series connected capacity and resistance elements, a phase shifting network comprising an electrical network including series connected capacity and resistance elements connected between a predetermined point on the resistor element which is connected between the anode of the first electron path and said point of predetermined potential and a predetermined point on the resistor connected between the anode of the second electron path and said point of predetermined potential and a second phase shifting network also including series connected capacity and resistance elements connected between similar points on the said resistance elements which are connected between the anodes and the point of predetermined potential of the third and fourth electron paths, a connection from the junction. point of. the capacity and resistance elements of each of said electrical networks to the control electrode. included within one electron path of each of the pairs, a connection between the control electrode of, the uncontrolled electron path to the point of predetermined potential, uni-control means for simultaneously varying the value of the resistance element of each of said series phase shifting networks to alter thereby the oscillation frequency developed, and a load circuit for deriving energy from. said circuit.

ALBERT L.v G. DE BEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,006,872 Nyman July 2, 1935 2,076,368 Fyler Apr. 6, 1937 2,171,670 Parker Sept. 5, 1939 2,149,471 Shore Mar. 7, 1939 2,154,492 Clough Apr. 18, 1939 2,017,708 Bedford Oct. 15., 1935 2,067,679 Puddle Jan. 12, 1937 

